Micro-annulus cracking or channeling is a major issue faced in the installation and use of oil and gas wells. Micro-annulus cracks are often formed between a well casing and a surrounding sleeve of concrete. The cracks are thought to result from fluctuations in the well casing, e.g. expansion/contraction thereof as pressures and temperatures change inside of the well casing change during installation and use. The cracks or channels provide a pathway through which fluids and/or gases can travel along the exterior of the well casing which may result in cross-contamination between vertically stratified zones of the well.
Oil and gas wells, among other well types, are commonly formed by first drilling a borehole in the ground and into a desired underground formation, e.g. a geologic formation holding oil, gas, or other resources. A well casing, which commonly comprises a steel pipe, is inserted into the borehole. Cement is then pumped through the well casing to fill the borehole around the well casing from the bottom up. A fluid, such as water or saline, is pumped into the well casing to displace the cement from within the well casing and a predetermined period of time is allowed to elapse to allow the cement to cure. The fluid can then be removed from the well casing to enable final preparation of the well casing before production of the desired resource begins. Such final preparations may include perforating and formation stimulation, eg. Acidizing and fracking the well at predetermined depths associated with the underground formations, among others.
Installation and removal of cement and fluid in the well casing may cause the well casing to expand and/or contract diametrically. However, the surrounding cement sleeve is not subjected to the same expansion/contraction, at least not to the same degree, as the well casing. The well casing may thus pull away from the cement sleeve at one or more locations along the length and/or circumference of the casing to form one or more micro-annulus cracks or channels therebetween. For example, removal of the displacement fluid from the well casing reduces or eliminates the hydrostatic pressure within the well casing and may thus allow the well casing to at least partially contract away from the cement sleeve.
A variety of attempts have been made to prevent micro-annulus cracking and/or to prevent fluid or gas movement through the cracks. For example, U.S. Pat. No. 3,064,731 to Hall discloses baffles that are installed on a well casing above and below a fracturing point. The baffles extend radially outward from the casing and aids in blocking or diverting a shockwave produced during fracturing of the well casing to protect adjacent areas of the casing and surrounding concrete from damage.
U.S. Pat. No. 3,387,656 to Guest et al. describes an elastomeric ring that is applied to the exterior of the well casing to provide a flexible seal between the concrete and the casing to block fluid flow therebetween. U.S. Pat. No. 3,802,500 to Schmidt describes fluid diverting baffles that include a cylindrical sleeve with a resilient annular flange extending radially outward therefrom. The outer diameter of the annular flange is slightly larger than bore hole such that the flange will be slightly upwardly cupped when installed in the borehole and can be forced into a downwardly cupped orientation by applying a pressure differential to allow downward fluid flow without excessive restriction.
Several attempts employ expandable or inflatable components or materials that fill a space between a well casing and sides of the bore hole or cement sleeve. For example, U.S. Pat. No. 4,440,226 to Suman describes inflatable sleeves that are placed on the casing to form a seal between the casing and the wall of the borehole. U.S. Pat. No. 4,716,965 to Bol et al. describes elastomeric foam sheaths that are installed on the exterior of a well casing to seal off any spacing between the casing and surrounding concrete. U.S. Pat. No. 7,631,695 to Schafer et al. describes an isolation tool that is disposed on the exterior wall of a casing and that includes a pair of chambers. The chambers contain two separate materials that can be dispensed from the isolation tool to mix and form a barrier to fluid flow, e.g. the materials chemically react when mixed. And U.S. Pat. No. 7,690,437 to Guillot et al. describes a device that is disposed on the exterior of a casing and that can be expanded after insertion of the casing in a bore hole to cause the device to fill the annular space around the casing and to inhibit the flow of fluids.
What is needed is a device that is simple in construction, is easily installed on a well casing, and that prevents or resists formation of continuous micro-annulus cracks or channels that extend between vertically stratified zones of a wellbore and that obstructs travel of fluids and gases between such zones.